I. Product Positioning: High-Rigidity Bearings for Compact Spaces and Combined Loads

In high-end equipment such as industrial robot joints, CNC rotary tables, medical manipulators and semiconductor equipment, bearings face the harsh challenge of extremely limited space combined with complex multi-directional loads. Traditional ball bearings carry loads through point contact. Under heavy loads or overturning moments, stress concentration occurs at contact points, causing local deformation of raceways. This deformation is amplified by the arm length, manifesting as perceptible trajectory deviation and jitter at the robot end-effector.

 

Crossed roller bearings are precisely designed to address these challenges. Developed with Japanese precision bearing design and manufacturing experience, NMT crossed roller bearings feature cylindrical rollers arranged at 90° perpendicularly in V-shaped raceways, expanding contact from points to lines and allowing stress to disperse evenly across raceway surfaces like flowing water. A single bearing simultaneously withstands radial loads, axial loads and tilting moments—equivalent to integrating the functionality of two angular contact bearings into the width of a single bearing, while significantly saving axial space. Robot wrists or positioners no longer need to stack multiple bearings to disperse loads—a single NMT crossed roller bearing is sufficient.

 

The line-contact structure delivers rigidity 3-4 times higher than conventional ball bearings. The ultra-thin cross-section design minimises inner and outer ring dimensions, approaching the limit of miniaturisation. The central hollow passage allows cables and tubes to pass straight through, eliminating the fatigue fracture risk from repeated bending. The axial space saved can be allocated to cables, air tubes or even force sensors, enabling robot bodies to maintain high rigidity while possessing more powerful end-integration capabilities. The overall machine appearance can thus be made more sleek and slender, and joint range of motion is no longer constrained by external cables.

 

II. Core Technology: Crowning Control, Negative Clearance Preload and Flexible Cages

(1) Roller Crowning Profile and Stress Control

 

Through strict control of roller crowning profiles and raceway surface integrity, NMT effectively reduces stress peaks in rolling contact areas. Even after millions of alternating load cycles, bearing rotational accuracy remains stable and clearances do not gradually increase. During manufacturing, NMT precisely calculates and machines roller crowning to ensure uniform load distribution across the full contact range, avoiding early fatigue from edge stress concentration.

 

(2) Negative Clearance Preload Technology

 

True precision motion cannot exist without strict management of "clearance." Ordinary bearings must reserve clearance for smooth assembly, but this微小间隙 is amplified by arm length into significant positioning deviation at the robot end-effector. NMT's approach is to implement negative clearance preload during crossed roller bearing manufacturing—through precision matching of inner and outer rings, rollers operate with zero clearance or even slight interference. This preload is not achieved through elastic deformation hard挤压, but based on NMT's precise calculation of raceway profiles and roller crowning, ensuring friction torque fluctuations are controlled within an extremely narrow range throughout the entire rotation cycle. For industrial robots that need to repeatedly perform welding or assembly at the same point, this means every positioning action reproduces the same posture without random angular drift.

 

(3) Flexible Pocket Cage Design

 

NMT's unique process for rolling consistency in crossed roller bearings uses flexible pocket structures enabling smooth re-establishment of contact during direction changes rather than sudden impact, effectively suppressing torque fluctuations. Spacers or separators between rollers prevent tilting or mutual friction, effectively avoiding abnormal increases in rotational torque. During high-speed operation or frequent motion direction changes, this design keeps rollers stable with torque fluctuations effectively controlled.

 

(4) Raceway Online Dynamic Balance Correction

 

During raceway grinding, NMT measures workpiece imbalance in real time and applies反向 compensation, ensuring uniform mass distribution of finished rings and minimising periodic excitation forces at high speeds.

 

III. Structural Classification and Functional Advantages

NMT crossed roller bearings offer four standard structural types, adapting to different precision and installation requirements:

 

(1) RB Series – Outer Ring Split Type

 

Outer ring split with integrated inner ring design, suitable for applications requiring high inner ring rotational accuracy. Rollers are arranged perpendicularly in V-shaped raceways separated by spacers. The split structure allows precise clearance adjustment, enabling high-accuracy rotational motion even under preload. Suitable for collaborative robot wrists, medical manipulators and other applications with extreme precision requirements.

 

(2) RE Series – Inner Ring Split Type

 

Inner ring split with integrated outer ring design, suitable for applications requiring high outer ring rotational accuracy. Main dimensions are the same as RB series, catering to different rotational accuracy requirements.

 

(3) RU Series – Integrated Inner and Outer Ring Type

 

Both inner and outer rings are integrated structures with pre-machined mounting holes, eliminating the need for fixing flanges and support housings. Installation has minimal impact on performance, providing stable rotational accuracy and torque. The high-rigidity integrated design with optimised mounting hole layout effectively reduces deformation caused by installation bolts, further enhancing rotational stability and precision, suitable for applications where both outer and inner rings rotate.

 

(4) RA Series – Ultra-Thin Compact Type

 

A new type derived from RB series design, with inner and outer ring thickness reduced to the limit. Most suitable for applications requiring lightweight and compact design, such as collaborative robots, humanoid robot wrists and ankles, precision alignment platforms and more.

 

Quick-Change Robot Special Design: NMT's crossed roller bearings for quick-change robots integrate high-hardness locating tapers on inner and outer rings. Through precision grinding, these tapers form self-centring rigid connections with matching taper holes on robot interfaces. Even after thousands of quick-change cycles, bearing installation positions remain repeatable to micron-level accuracy without incremental compensation of tightening torque. This design, which transfers positioning functionality from the housing to the bearing itself, enables modular robots to maintain joint rigidity while achieving true plug-and-play flexibility.

 

General advantages summary: Orthogonally arranged cylindrical rollers with line-contact high rigidity, 3-4 times higher than ball bearings; single bearing handling radial, axial and tilting moment loads; ultra-thin cross-section design providing reliable support with minimal height; central hollow for cable routing; negative clearance preload eliminating clearance amplification effects, ensuring repeat positioning accuracy; strict control of roller crowning profiles and raceway surface integrity effectively reducing stress peaks; full-lifecycle precision retention capability; split structure allowing precise clearance adjustment; precision grades covering P5/P4/P2.

 

IV. Two-Grade Material & Process Selection

Grade 1: Through-Hardened Bearing Steel (General Version)

 

Integral quenching and low-temperature stabilizing tempering achieve uniform raceway hardness and excellent roller wear resistance. Suitable for general industrial robot joints, automation turntables, precision testing equipment and other conventional conditions, with outstanding cost performance for mass production supporting.

 

Grade 2: Carburized Bearing Steel (Heavy-Duty Reinforced Version)

 

Inner rings, outer rings and rollers undergo deep carburizing quenching for hard wear-resistant surfaces with a tough impact-absorbing core. Applied to heavy-duty palletising robots, large six-axis robots, humanoid robot hips and other high-load applications, withstanding instantaneous peak loads with significantly extended service life under extreme conditions.

 

V. Japanese Precision Manufacturing Process

Vacuum degassing refining of high-purity special steel forging, controlling non-metallic inclusions to extremely low levels and eliminating fatigue crack initiation points;

 

Precision forging + gradient heat treatment, ensuring thin-section rings maintain stable geometric shapes after quenching, preventing warpage from residual stress release;

 

Staged stabilisation treatment precisely coordinated with ultra-precision grinding—thin-section rings are prone to residual stress release and distortion after grinding; NMT employs staged stabilisation treatment precisely coordinated with ultra-precision grinding to bring raceway roundness and roughness to demanding levels;

 

Precise roller crowning profile control—strictly controlling roller crowning curves and raceway surface integrity to effectively reduce stress peaks in rolling contact areas;

 

Flexible pocket cage design—NMT's unique process for rolling consistency in crossed roller bearings uses flexible pocket structures enabling smooth re-establishment of contact during direction changes rather than sudden impact, effectively suppressing torque fluctuations;

 

Raceway online dynamic balance correction—real-time measurement and compensation of workpiece imbalance during grinding, ensuring uniform mass distribution of finished rings;

 

Group matching of rollers with micron-level dimensional tolerance control for uniform load distribution;

 

Superfinishing and mirror-grade polishing of raceways with stable surface roughness control for stable lubricating oil film formation;

 

Assembly in temperature-controlled dust-free workshops with precise preload and clearance control;

 

100% full inspection including torque, vibration, rotational accuracy and run-in tests, with complete data archived.

 

All dimensions comply with international standards for direct interchange with mainstream crossed roller bearings. Low-temperature sulphurising surface treatment is available for high-humidity or salt-spray environments, forming a self-healing sulphide film on roller and raceway surfaces that isolates corrosive media from the metal substrate.

 

VI. Precision Grades & Customisation Options

P5 Grade: General precision grade, suitable for most industrial robot joints and automation turntables;

 

P4 Grade: High precision grade, suitable for precision testing equipment, optical instruments and medical imaging equipment;

 

P2 Grade: Ultra-high precision grade, suitable for semiconductor equipment, aerospace-grade precision rotation mechanisms.

 

Customisation options: special clearance configurations, high/low temperature resistant materials, special grease adaptation, non-standard sizes, integrated locating taper design, contact/non-contact labyrinth seal options, low-temperature sulphurising corrosion-resistant surface treatment, topology-optimised lightweight customisation and more.

 

VII. Wide Application Fields

Industrial Robots: Bases, shoulders, elbows, wrists, finger joints—high-rigidity compact support; robot reducer and joint housing interface;

Collaborative & Humanoid Robots: Wrists, ankles, hips—dual requirements of thin-section and rigidity;

Medical Equipment: Surgical robot bases, CT scanner slip ring systems, rehabilitation equipment rotary platforms;

Semiconductor Equipment: Wafer handling robots, vacuum transfer chambers, IC manufacturing equipment rotary platforms;

Precision Testing Equipment: Precision test turntables, optical telescopes, large radar antennas;

Laser Processing Equipment: Laser cutting machine turntables, LiDAR scanning mechanisms;

CNC Machine Tools: Machining centre rotary tables, indexing plates, precision rotary worktables;

Aerospace: Satellite antenna azimuth drives, missile launcher slewing devices;

General Machinery: DD motors, robotic rotating sections, precision alignment platforms.

 

VIII. Brand Supply & Customisation Service

NMT maintains sufficient spot inventory of mainstream crossed roller bearing specifications for urgent equipment repair and mass complete machine supporting with short lead time. Customisation services include P4/P2 high precision grades, special clearance, high/low temperature resistant materials, special grease, non-standard sizes, integrated locating taper design, contact/non-contact labyrinth seal options, low-temperature sulphurising corrosion-resistant surface treatment, topology-optimised lightweight customisation and more. Professional engineers provide targeted selection schemes based on equipment load spectrum, installation space, accuracy requirements and speed range to optimise bearing configuration and structural selection, improve overall machine rigidity, control end-effector jitter, extend precision retention cycles and cut the overall life cycle cost of equipment.